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Cannabis valuation – art or science?

June 01 2010

Cannabis yield estimations are used in criminal cases where the charges may include possession with intent to supply and cultivation/production of a Class B drug. They are also used to form the basis of the calculations in Proceeds of Crime Act (POCA) applications.

Following the fragmentation of forensic supply to the prosecution there are now several forensic providers each with their own approach to cannabis yield calculations. The methodology behind the yield estimation may be different from that seen previously. This can affect the drug valuation significantly. If the valuation appears to be excessive to you or your client, you may consider that expert comment on the protocol used would benefit your case. Successful challenges have been made on this basis.

There are a number of attributes of cannabis cultivation that should be taken into consideration when estimating cannabis yield and valuation. An important factor is the number, condition and development stage of plants being considered. Usually, the police scene photographs or DVD will be available for examination. It is important to view the photographic evidence as it can provide vital clues as to the sophistication of the setup and the skill or experience of the grower. How this information is considered varies between the Crown’s forensic providers. One provider in particular will insist on viewing the scene photographs/DVD before providing yield estimates whilst others are not so aware of the importance of this evidence. In the absence of a scientific yield estimate, police drugs officers have been tempted to provide their own yield estimates with apparently no scientific basis for their opinions.

Once seized, a representative sample of the plants should have been sent to one of the forensic providers together with an indication of the total number of plants at the scene. The scientist will measure the yield from the sample plants and extrapolate to calculate a potential yield for the entire crop. In the case of immature plants they will revert to their own studies of previous cases where mature plants have been harvested and then apply these figures to provide a yield estimate.

In making this extrapolation from sample to whole crop, the scientist should make a reasoned judgment on various aspects of the scene such as: How successful has the grower been? Is the sample received representative of the likely final crop? Are all the plants in the same healthy condition? If the scene includes plants at early stages of maturity, what proportion of these will yield the same as that measured from the sample plants? Will the setup support the number of cuttings being cultivated?

Finally, the calculated yield is reported to the police to prepare a valuation. The concept of a discount for bulk supply will be familiar and equally applies in the supply of drugs. In general, the police will report their valuation on the basis of street prices as if the drug were to be sold in the smallest possible deals. When considering the value of large amounts of cannabis, the street valuation may provide an unrealistically high estimate for the drug. This artificially high figure can be passed through the courts and, without challenge, can significantly affect sentencing and POCA applications which may follow.

In summary, estimating cannabis yield is more complex than simple measurement and multiplication. It is usually worthwhile taking a closer look at the calculated yield and valuations prepared by the Crown. In many cases this can make the difference between a conviction for personal use only and supply; and in the case that supply is accepted, the difference between custodial and non-custodial sentences.


Richard Brown

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